The present invention relates to electric power conversion systems, and more particularly, to switched mode energy storage DC-DC electric power conversion systems capable of providing power to a plurality of electric power systems.
Electric power systems, such as those found on vehicles and aircraft, often are used to produce electric power for different kinds of on-board electronic equipment having different functions and electrical requirements. For example, battery chargers and motors, such as those used for starters in auxiliary power units, may require different voltages, currents and polarities.
Electric power conversion systems are used to supply subsystems with the required electrical energy by converting electrical energy from a main generator into the specific form needed. Where electrical subsystems have very different functions and power transfer directions, such as starters and motors, more than one electric power conversion systems may be needed. Multiple power conversion systems may also be needed to provide electrical isolation between different subsystems.
There are a number of drawbacks with using multiple power conversion systems. The multiple units may add to the overall system cost. System performance can be degraded by the additional weight and volume. Also, the additional electrical components can reduce reliability and lower efficiency.
Where dual voltages are required to be transferred in two directions between two voltage subsystems, bi-directional dc-dc converters are one type of converter that can operate in two directions. Bi-directional dc-dc converters are energy storage converters which are based on the implementation of energy transfer cycles. These cycles may include a period of accumulation of magnetic energy in an inductive component, via a primary circuit, followed by a period of restitution of this energy into a load to be supplied, via a secondary circuit. Bi-directional converters can transfer energy from the primary circuit to the secondary circuit as well as from the secondary circuit to the primary circuit. Such bi-directional converters are particularly well suited to the supplying of complex loads (capacitive and/or inductive loads), accumulators or, further, reversible devices such as electric motors, which are likely to send energy back to the power source.
A “buck-boost” converter is one type of bi-directional converter, the inductive component of which is a single-winding inductance. U.S. Pat. No. 4,746,151 shows an example of a “buck-boost” converter. A “fly-back” converter is a converter, where the inductive component is a transformer including at least two windings. U.S. Pat. No. 3,986,097 shows one example of an energy storage bi-directional “fly-back” converter.
Prior bi-directional dc-dc converters can suffer from one or more of the following problems: high switching losses, necessity of an isolated feedback, difficult no-load control, and low efficiency due to losses in the output rectifier, particularly with low output voltages. Because of these problems, bi-directional converters are best suited for low power applications.
As can be seen, there is a need for a converter that can meet the needs of a plurality of power conversion systems having different functions and power transfer directions. There is also a need for a converter which minimizes the duplication of components to achieve improvements in volume, weight, reliability and efficiency. There is a further need for a bi-directional dc-dc converter that can handle high power requirements, and provide isolation with minimum switching losses.